In some roller type one-way clutches, a locked state in which the inner ring and the outer ring are locked by rollers is released by moving the rollers by a movable retainer in a an unlocking direction (see e.g. patent literature 1). Such one-way clutches are used, for example, to control rotational position. In some cases, such one-way clutches are used as inverse input blocking clutches as disclosed in patent literature 2.
FIG. 4A is a partial cross sectional view of a conventional one-way clutch in the locked state seen from an axial direction. FIG. 4B is a cross sectional view taken along line b-b in FIG. 4A. FIG. 5 is a partial cross sectional view of the conventional one-way clutch in an unlocked state seen from the axil direction. In FIG. 4A, the right rotation direction of the one-way clutch and the rollers will be referred to as the clockwise direction, and the left rotation direction will be referred to as the anticlockwise direction. As to the circumferential directions also, the right rotation direction will be referred to as the clockwise direction, and the left rotation direction will be referred to as the anticlockwise direction.
The one-way clutch 301 shown in FIG. 4A has an inner ring 305 having an outer circumferential surface 307 on which recesses 311 recessed radially inwardly are provided. A cylindrical roller 319 is provided in each recess 311 in such a way as to be capable of rotating or sliding along the circumferential direction.
The radial distance between the bottom of the recess 311 and the inner circumferential surface 309 of the outer ring is larger than the diameter of the roller 319. The bottom surface 323 of the recess 311 is a curved surface that is inclined in such a way that the distance between the bottom surface 323 and the inner circumferential surface 309 of the outer ring decreases as it extends in the anticlockwise direction. Thus, the bottom surface 323 of the recess 311 and the inner circumferential surface 309 of the outer ring radially opposed to it define a wedge-shaped space W301 therebetween. The radial dimension of the wedge-shaped space 301 is smaller than the diameter of the roller 319. The bottom surface 323 of the recess 311 serves as a cam surface with which the roller engages.
The one-way clutch 301 includes a fixed retainer 327 fixed to the inner ring 305 and a movable retainer 333 that is movable relative to the inner ring 305. The fixed retainer 327 has a plurality of fixed retaining parts 331 arranged at regular intervals along the circumferential direction between the inner ring 305 and the outer ring 303. The movable retainer 333 has a plurality of movable retaining parts 337 arranged at regular intervals along the circumferential direction between the inner ring 305 and the outer ring 303. The fixed retaining parts 331 and the movable retaining parts 337 are arranged alternately along the circumferential direction as shown in FIG. 4A. The fixed retaining part 331 is arranged on the clockwise side of each roller 319, and the fixed retaining part 337 is arranged on the anticlockwise side of each roller 319.
In the state shown in FIG. 4A, the roller 319 is biased toward the anticlockwise direction by a spring provided on the anticlockwise end of the fixed retaining part 331, so that the roller engages with the bottom surface 323 serving as a cam surface and the inner circumferential surface 309 of the outer ring on the anticlockwise side. In this state, the inner ring 305 and the outer ring 303 is in a locked state, preventing rotation of the inner ring 305 in the clockwise direction.
As shown in FIG. 5, when releasing the locked state in which the inner ring 305 and the outer ring 303 are locked, the movable retaining parts 337 of the movable retainer 333 move clockwise toward the rollers 319 as indicated by an arrow D31 to come in contact with the rollers 319 and push the rollers 319 in the clockwise direction as indicated by an arrow D32 in FIG. 5. Consequently, the rollers 319 turn in the clockwise direction while rolling or sliding on the respective cam surfaces 323 and the inner circumferential surface 309 of the outer ring. Rolling or sliding of the rollers 319 on the respective cam surfaces 323 causes the inner ring 305 to turn in the unlocking direction. In this state, the rollers 319 are disengaged from the inner ring 305 and the outer ring 303 as shown in FIG. 5, thereby releasing the engagement of the inner ring 305 and the outer ring 303. Thus, the locking of the inner ring 305 and the outer ring 303 is released, allowing the inner ring 305 to turn in the clockwise direction.